1 /* Copyright (c) 2007-2023. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_MC_UDPOR_MAXIMAL_SUBSETS_ITERATOR_HPP
7 #define SIMGRID_MC_UDPOR_MAXIMAL_SUBSETS_ITERATOR_HPP
9 #include "src/mc/explo/udpor/Configuration.hpp"
10 #include "src/xbt/utils/iter/iterator_wrapping.hpp"
12 #include <boost/iterator/iterator_facade.hpp>
16 #include <unordered_map>
18 namespace simgrid::mc::udpor {
21 * @brief An iterator over the tree of sets of (non-empty) maximal events that
22 * can be generated from a given set of events
24 * This iterator traverses all possible sets of maximal events that
25 * can be formed from some subset of events of an unfolding,
26 * each of which satisfy a predicate.
28 * Iteration over the maximal events of a configuration is an important
29 * step in computing the extension set of a configuration for an action
30 * whose identity is not "exploitable" (i.e. one whose type information cannot
31 * help us narrow down our search).
33 struct maximal_subsets_iterator
34 : public boost::iterator_facade<maximal_subsets_iterator, const EventSet, boost::forward_traversal_tag> {
36 // A function which answers the question "do I need to consider maximal sets
37 // that contain this node?"
38 using node_filter_function = std::function<bool(const UnfoldingEvent*)>;
39 using topological_order_position = std::vector<const UnfoldingEvent*>::const_iterator;
41 maximal_subsets_iterator() = default;
42 explicit maximal_subsets_iterator(const Configuration& config) : maximal_subsets_iterator(config.get_events()) {}
43 explicit maximal_subsets_iterator(const EventSet& events) : maximal_subsets_iterator(events, std::nullopt) {}
45 maximal_subsets_iterator(const Configuration& config, std::optional<node_filter_function> filter)
46 : maximal_subsets_iterator(config.get_events(), filter)
49 maximal_subsets_iterator(const EventSet& events, std::optional<node_filter_function> filter);
52 std::vector<const UnfoldingEvent*> topological_ordering;
54 // The boolean is a bit of an annoyance, but it works. Effectively,
55 // there's no way to distinguish between "we're starting the search
56 // after the empty set" and "we've finished the search" since the resulting
57 // maximal set and backtracking point stack will both be empty in both cases
58 bool has_started_searching = false;
59 std::optional<EventSet> current_maximal_set = std::nullopt;
60 std::stack<topological_order_position> backtrack_points = std::stack<topological_order_position>();
63 * @brief A small class which provides functionality for managing
64 * the "counts" as the iterator proceeds forward in time
66 * As an instance of the `maximal_subsets_iterator` traverses
67 * the configuration, it keeps track of how many events
68 * further down in the causality tree have been signaled as in-conflict
69 * with events that are its current maximal event set (i.e.
70 * its `current_maximal_set`)
74 using topological_order_position = maximal_subsets_iterator::topological_order_position;
76 void mark_included_in_maximal_set(const UnfoldingEvent*);
77 void mark_removed_from_maximal_set(const UnfoldingEvent*);
78 topological_order_position find_next_candidate_event(topological_order_position first,
79 topological_order_position last) const;
82 std::unordered_map<const UnfoldingEvent*, unsigned> event_counts;
84 /// @brief Whether or not the given event, according to the
85 /// bookkeeping that has been done thus far, can be added to the
86 /// current candidate maximal set
87 bool is_candidate_event(const UnfoldingEvent*) const;
90 void add_element_to_current_maximal_set(const UnfoldingEvent*);
91 void remove_element_from_current_maximal_set(const UnfoldingEvent*);
94 * @brief Moves to the next node in the topological ordering
95 * by continuing the search in the tree of maximal event sets
96 * from where we currently believe we are in the tree
98 * At each stage of the iteration, the iterator points to
99 * a maximal event set that can be thought of as `R` + `A`:
104 * where `R` is some set of events and `A` is another event.
106 * The iterator first tries expansion from `R` + `A`. If it finds
107 * node `B` to expand, this means that there is a node in the tree of
108 * maximal event sets of `C` (the configuration traversed) such that
109 * `R` + `A` + `B` needs to be checked.
111 * If no such node is found, then the iterator must check `R` +
112 * some other node AFTER `A`. The new set of possibilities potentially
113 * includes some of `A`'s dependencies, so their counts are decremented
114 * prior to searching.
116 * @note: This method is a mutating method: it manipulates the
117 * iterator such that the iterator refers to the next maximal
118 * set sans the element returned. The `increment()` function performs
119 * the rest of the work needed to actually complete the transition
121 * @returns an iterator poiting to the event that should next
122 * be added to the set of maximal events if such an event exists,
123 * or to the end of the topological ordering if no such event exists
125 topological_order_position continue_traversal_of_maximal_events_tree();
127 // boost::iterator_facade<...> interface to implement
129 bool equal(const maximal_subsets_iterator& other) const { return current_maximal_set == other.current_maximal_set; }
130 const EventSet& dereference() const
132 static const EventSet empty_set = EventSet();
133 if (current_maximal_set.has_value()) {
134 return current_maximal_set.value();
139 // Allows boost::iterator_facade<...> to function properly
140 friend class boost::iterator_core_access;
143 using maximal_subsets_iterator_wrapper =
144 simgrid::xbt::iterator_wrapping<maximal_subsets_iterator, const Configuration&>;
146 } // namespace simgrid::mc::udpor